Molding is a process by virtue of which a molded article can be formed from molding material by using a molding system. Various molded articles can be formed by using the molding process, such as an injection molding process. One example of a molded article that can be formed, for example, from polyethylene terephthalate (PET) material is a preform that is capable of being subsequently blown into a beverage container, such as, a bottle and the like.
A typical molding system includes, amongst other things, an injection unit, a clamp assembly and a mold assembly. The injection unit can be of a reciprocating screw type or of a two-stage type. The clamp assembly includes, amongst other things, a frame, a movable platen, a fixed platen and an actuator for moving the movable platen and to apply tonnage to the mold assembly arranged between the fixed and movable platens. The mold assembly includes, amongst other things, a cold half and a hot half. The hot half is usually associated with one or more cavities (and, hence, also sometimes referred to by those of skill in the art as a “cavity half”), while the cold half is usually associated with one or more cores (and, hence, also sometimes referred to by those of skill in the art as a “core half”). The one or more cavities together with one or more cores define, in use, one or more molding cavities. The hot half can also be associated with a melt distribution system (also referred to sometimes by those of skill in the art as a “hot runner”) for melt distribution. The mold assembly can be associated with a number of additional components, such as neck rings, neck ring slides, ejector structures, wear pads, etc.
As an illustration, the injection molding of a preform, of the type that is later blow molded into a bottle, typically involves the heating of a molding material, such as, for example, PET, to a homogeneous molten state and injecting, under pressure, the so-melted molding material into the one or more molding cavities defined, at least in part, by the aforementioned one or more cavities and one or more cores mounted respectively on a cavity plate and a core plate of the mold assembly. The cavity plate and the core plate are urged together and are held together by clamp force, the clamp force being sufficient enough to keep the cavity and the core plates together against the pressure of the injected molding material. The molding cavity has a shape that substantially corresponds to a final cold-state shape of the molded article to be molded. The so-injected molding material is then cooled to a temperature sufficient to enable ejection of the so-formed molded article from the mold. When cooled, the molded article shrinks inside of the molding cavity and, as such, when the cavity and core plates are urged apart, the molded article tends to remain associated with the core. Accordingly, by urging the core plate away from the cavity plate, the molded article can be demolded, i.e. ejected from the core piece. Ejection structures are known to assist in removing the molded articles from the core halves. Examples of the ejection structures include stripper plates, ejector pins, etc.
One consideration for economical operation of the molding system is cycle time or, in other words, time that elapses between a point in time when the cavity and core halves are closed and the molded articles are formed and a subsequent point in time when they are opened and the molded articles are removed. As one will appreciate, the shorter the cycle time, the higher the number of molded articles that can be produced in a particular mold of a given size in a given time interval. Accordingly, injection molding systems are commonly provided with one of more post-mold treatment devices wherein a so-called “post-mold treatment” process is performed for sake of minimizing the molding cycle time and/or for ensuring that the molded article produced remains substantially defect free. Generally speaking, the post-mold treatment process involves transferring the molded articles from the mold, once they are sufficiently cooled to enable ejection thereof, to the post-mold treatment device. A post-mold treatment of the molded articles, commonly the continued cooling thereof, then ensues in the post-mold treatment device. The post-mold treatment generally occurs independently (but in parallel) to the injection cycle of the molding machine.
An example of the post-mold treatment device is disclosed in a commonly assigned U.S. Pat. No. 7,104,780 issued to Domodossola et al. on Sep. 12, 2006. More specifically, Domodossola et al. discloses a post-mold treatment device that is mounted to a platen of an injection molding machine, the post-mold treatment device being configured for handling and cooling molded articles received from an injection mold.
It is quite common to equip the post-mold treatment device, such as those provided with preform molding systems from Husky Injection Molding Systems Limited, with a so-called take-off plate having an arrangement of post-mold preform receptacles with which the molded articles are to be received from the mold. Such post-mold preform receptacles are generally configured in accordance with the teachings of commonly assigned U.S. Pat. No. 4,729,732 issued to Schad et al. on Mar. 8, 1988. The foregoing '732 patent describes the post-mold preform receptacle as a carrying means for holding and cooling a heated parison (i.e. preform) therein. The carrying means having an open forward end for receiving the parison, a closed rearward end, a longitudinal wall between the forward and rearward ends with an internal surface tapering inwardly towards the closed end. There is also a cooling means adjacent the longitudinal surface. The internal surface is smaller than the heated parison, the parison also having a corresponding taper so that the cooling means is operative to shrink the parison upon cooling with the parison sliding inside the tube to fit snugly therein. The carrying means further including suction means adjacent the closed end for maintaining the cooled parison inside the tube.
Another patent that describes a post-mold preform receptacle for use with a post-mold device is commonly assigned U.S. Pat. No. 7,264,464 issued to Unterlander et al. on Sep. 4, 2007. The '464 patent reviews, amongst other things, the common general knowledge that those skilled in the art will appreciate the selection of an relation to be applied to the inner mating surface varies as a function of the shape of the preform and the related injection molding process.
A recently published post-mold treatment process for post-mold cooling of molded articles, such as preforms and the like, is described in commonly assigned PCT patent publication 2007/143815 to Niewels published on Dec. 21, 2007, and henceforth referred to in this specification as the “balanced cooling rate post-mold treatment process”. The process involves a post-mold cooling of a molded article, such as a perform, the molded article having just been molded within mold halves of a mold. The process includes receiving, in a post-mold device, the molded article and subjecting the molded article to post-mold cooling. The post-mold cooling including balancing cooling rates during the post-mold cooling so that the molded article reaches a target exit temperature at a point of time that substantially coincides with a point of time when the molded article is removed from the post-mold cooling, the target exit temperature that substantially precludes post-ejection defects. Put another way, the process moves away from the main stream thought of simply cooling a received portion of the molded article as aggressively as possible to a process of controlling a cooling rate imposed on various portions of the molded article.